Just bought my '71 camaro last week and the MSD Pro Billet distributor is just like it came out of the box with 21 degrees of centrifical advance that's all in by 3500. Assuming I plan to run say 18 degrees of initial advance and change the springs to limit centrifical advance to 18 degrees for 36 total, what is a reasonable advance curve to dial in. I have always heard its better to bring centrifical advance in earlier, but how much earlier. Is there anything that I can use as a guide or do i just need to try different combinations? How does the fact that I am also running vacuum advance play into the ideal curve? I am running a 700R4 with 2400 stall and 3:42 gears.

You might want to read the info in the following 2 links. Lars Grimsrud is a former engineer with Chevy and is the acknowledged guru of timing and carb tuning. I spoke to him a couple of weeks ago about timing on my car and his general setup involves setting the dist up so that all advance is in by 25-2800 rpm, with a maximum of 36 degrees (38 if the cam is bigger). Total advance with initial, mechanical and vacuum should not exceed 52 degrees and vacuum advance should be plugged into full manifold vacuum. If your cam makes less than 15 in. Hg at idle, you may need to change the canister to one that will allow full vacuum advance at readings less than the 15 that is default with most stock canisters.

There is a lot of good info in the articles, and getting this right will probably go far toward getting your carb issues sorted out. Good luck.

http://www.hotrodders.com/forum/distributor-tuning-theory-part-1-a-59033.html

http://www.vettefinders.com/index.cfm/fuseaction/Vette101Story/ID/19

Thanks a lot for the 2 articles, I actual had come across the first one earlier and it definitely helped me understand all the theory. In the second he says if you run 36-38 total degrees and you experience denotation to retard the timing 2 degrees at a time until it stops. Does that mean to retard initial advance or mechanical advance, or does it matter? I guess if you run say 18 initial and 18 mechanical, you probabaly will be forced to retard initial since most distributors I have seen are not adjustable to lower than 18 degrees of mechanical advance.

Thanks for all your help...should be interesting to see what works...

Just checked my current vacuum at idle and its only 12 in. Hg. I guess I may need to change my vacuum canister since the one that came with my MSD Pro-Billet doesn't fully deploy until 15 in. Hg. It's supposed to give me 10° advance, but all I'm getting is 7°. Can anyone recommend a good replacment vacuum canister that will work with an MSD Pro-Billet but fully deploy at a lower vacuum level. I've seen a few posts referring to a NAPA/VC-1810 can that is fully deployed at 8 in. Hg and provides around 15° vacuum advance. Is anyone else running this can with success?

Also for some reason an MSD Tech was recommending use of "ported" vacuum with their distributors because and I quote..."This will have the most vacuum at idle and it should start to fall off as the engine goes under load." I always understood that "ported" vacuum was zero at idle and increased off idle and it was manifold vacuum that offered the most vacuum at idle and fell off as the engine goes under load. What am I missing here?

Will these techniques work when you have an unknown (presumed non-stock) cam?
My car cannot currently maintain an Idle at less than 800RPM. I don't know if this is the cam's fault or if it is just mis-timed. I'm new to this type of thing, just learning the theory behind keeping a recip engine trimmed properly.

You are not missing anything. I have run that same distributor with an engine that pulled 12" of vac and with manifold vacuum. What you want to verify is if the advance reading, with the vac line connected to manifold vacuum, is stable at idle. A degree or to is not an issue. 5 to 10 degrees is an issue.

We set those distributors up at 12 degrees of base and the silver bushing. The light blue and the light silver springs will bring all the advane in by about 3000 RPM.

If the compression is reasonable that should give you very good throttle response and put your total timing in the 36 to 37 degree range. That total should be within a degree or two of best power, so don't be afraid to play with it to that degree(s).

If it idles smooth with the vac on manifold port feel free to leave it there. If it doesn't, more to the ported and readjust the idle speed. The only difference is you won't have advance at idle but once you open the throttle the canister will kick in.

Thanks for all the reply posts!

Idel advance is relatively stable right now at 22 ° with manifold vacuum connected, 15° with the vacuum line plugged. I see the set up you (Rick) are running with the silver bushing (25° mechanical advance), 12 initial advance, light blue and light silver mechanical spring bringing it all in by 3000 RPM. Just curious why you set up with more mechanical advance than initial - I have always heard you should run as much initial advance as possible and just assumed you would then back into the rest in mechanical to reach 36-38 total?

Also have you had to deal with changing vacuum cans since at 12 in.Hg manifold vacuum you cannot fully deploy the MSD cannister to its full potential (I think it has a potential of 10° at 15 in Hg. - I assume that's in crankshaft degrees)?

At this point I am really just trying to sort all this and put together a plan of how to proceed. Hungry to learn all theory and put to work...